A conventional biped walking robot generates the pre-designed walk pattern (hereinafter to be called “gait”) data, conducts walk control according to said gait data, moves foot portions by the predetermined walk pattern, and thereby realizes biped walking.
However, such a biped walking robot tends to be unstable in walking posture upon walking due, for example, to road surface conditions, or the error of the robot's own physical parameters, or else, and may tumble down in some cases. On the other hand, if a robot is made to conduct walk control without pre-designed gait data while confirming walk conditions in real time, then walking is possible with stable walking posture, but even in such cases, the robot may tumble down with collapsed walking posture, when unexpected road conditions are encountered.
Therefore, what is called ZMP compensation is required, whereby the points on the sole of a foot of the robot where the composite momentum of floor reaction force and gravity becomes zero (hereinafter to be called ZMP “Zero Moment Point”) are converged to the target value. As such a control method for ZMP compensation, the method to accelerate and adjust the robot's upper body by utilizing compliance control and converging ZMP to the target value, as shown, for example, in JP 5-305583 A, or the control method to adjust the landing position of the robot's foot is known.
Incidentally, in such control methods, the stabilization of a robot is aimed by ZMP regulation, and in said ZMP regulation there should be a prerequisite to accurately detect floor reaction force at a sole.
However, as for a biped walking robot of such structure, there may be such cases where a whole sole does not land on the road surface in the unstable road condition with complex roughness, and floor reaction force at a sole can not be accurately detected, and thereby ZMP compensation can not be accurately conducted. For this reason, the robot's stability can not be maintained, and the robot's biped walking becomes difficult.